1. Field of the Invention
The present invention relates to a magnetic recording medium for use in heat-assisted magnetic recording in which writing is performed while the magnetic recording medium is heated to reduce its anisotropic magnetic field, and further to a magnetic recording apparatus provided with such a magnetic recording medium.
2. Description of the Related Art
As the recording density of a magnetic recording apparatus, such as a magnetic disk apparatus, becomes higher, further improvement has been required in the performance of a thin-film magnetic head and a magnetic recording medium. As the thin-film magnetic head, a composite-type thin-film magnetic head is widely used, which has a stacked structure of a magnetoresistive (MR) element for reading data and an electromagnetic transducer for writing data.
On the other hand, the magnetic recording medium is generally a kind of discontinuous body of magnetic microparticles gathered together. Here, one record bit consists of a plurality of the magnetic microparticles. Therefore, in order to improve the recording density, it is necessary to decrease the size of the magnetic microparticles and reduce irregularity in the boundary of the record bit. However, the decrease in size of the magnetic microparticles raises a problem of degradation of thermal stability of magnetization due to decrease in volume.
As a countermeasure to this problem, it is conceivable to increase the magnetic anisotropy energy KU of the magnetic microparticle. However, this increase of KU causes the increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. On the other hand, the upper limit of write-field intensity by the thin-film magnetic head is virtually determined by the saturation magnetic flux density of soft magnetic material constructing a magnetic core in the head. Therefore, the writing data becomes impossible if the anisotropic magnetic field of the magnetic recording medium exceeds a permissible value determined by the upper limit of write-field intensity.
As a method of solving this problem of thermal stability, so-called a heat-assisted magnetic recording technique is proposed, in which writing is performed by reducing the anisotropic magnetic field with heat supplied to the magnetic recording medium formed of magnetic material with large KU just before application of the write field. For the heat-assisted magnetic recording technique, such a method is a mainstream as disclosed in US Patent Publication No. 2004/081031 A1. The method includes providing an optical system within a thin-film magnetic head, and irradiating near-field light from the thin-film magnetic head on the magnetic recording medium.
However, a problem arises when providing an optical system for generating the near-field light within a thin-film magnetic head as described above, in that it is not easy to form each optical part and also considerably difficult to generate desired near-field light stably in the formed optical system.
Actually, an element for generating the near-field light has to be formed within the head while locating on a opposed-to-medium surface, while it is difficult to provide a light source, such as a laser diode, near the opposed-to-medium surface. Accordingly, when the light source is provided at a position separated apart from the opposed-to-medium surface, a waveguide is necessitated to efficiently propagate the light from the light source to the near-field light generating element. Here, the near-field light generating element, the waveguide and the light source have to have respective sufficient performances, and relative positional accuracy between the optical system and a write head element is required to be high enough. Hence, it has been worried that the yield of manufacturing thin-film magnetic heads may be lowered because it is very difficult to form an optical system having such sufficient performance.